Method for preparing of film of a vinylidene chloride polymer

ABSTRACT

A vinylidene chloride polymer film, a method of producing a direct laminate of vinylidene chloride and a non-saran thermoplastic polymer, preferably polyethylene, including procedures for orienting and irradiating the laminate and the method above wherein the outer polymer layers are stripped from the saran to provide a saran film.

United States Patent [191 Baird, Jr. et al.

[ METHOD FOR PREPARING OF FILM OF A VINYLIDENE CHLORIDE POLYMER [75]Inventors: William G. Baird, Jr., Winchester; Stanley E. Holbrook, SouthActon; Jeremy A. Platt, Cambridge, all of Mass.

[73] Assignee: W. R. Grace & C0., Cambridge,

Mass.

221 Filed: Feb.ll, 1971 21 Appl.No.:ll4,692

Related US. Application Data [62] Division of Ser. No. 590,107, June 2,1966, abandoned, which is a division of Ser. No. 157,194, Dec. 5, I961,abandoned.

[52] US. Cl ..260/9l.7,1l7/161,161/198, 161/199, 161/227, 161/231,1'61/254,

204/159.14, 260/785 UA, 260/855 XA,

[51] int. Cl. C08f 15/06 [58] Field of Search 260/91.7, 87.7

in] 3,821,182 June 28, 1974 [56] References Cited UNITED STATES PATENTS2,233,442 3/1941 Wiley 260/917 2,309,370 l/l943 Williams 260/91.72,332,489 10/1943 Reinhardt et a1, 260/9l.7 2,3445] 1 3/1944 Harder260/9l.7 2,354,435 7/1944 Stedman 260/9l.7 2,405,008 7/1946 Berry1260/91.?

Primary Examiner -l-larry Wong, Jr. Attorney, Agent, or Firm-John J.Toney; William D. Lee, Jr.

5 Claims, 7 Drawing Figures mammmz 1914 3821' 18-2 SHEET 3 OF 3 I 206202; E u o U 2.0

Fig.7

This application is a division of my prior copending application Ser.No. 590,107, filed on June 2, 1966 which was a division of Ser. No.157,194, filed Dec. 5, 1961, now both abandoned.

This invention relates to novel saran products and methods of making thesame.

It is an object of the present invention to prepare an unoriented filmof vinylidene chloride polymer having improved physical characteristics.

Another object is to prepare an extruded saran film free from blemishesdue to die scratches and/or film handling mechanisms.

A further object is to prepare saran films having high gloss andclarity.

An additional object is to devise a simple and efficient process forpreparing extremely thin saran film.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that these objects can be accomplished by meltextruding a ply of saran with a ply of another extrudable, thermoplasticpolymer other than saran. Thereafter, the thermoplastic ply is strippedfrom the saran ply in the preferred form of the invention. Frequently,it is advantageous to have both sides of the saran ply covered by a plyof a thermoplastic resin other than saran. In such case both of theouter non-saran thermoplastic plies can be stripped from the centersaran ply.

The melt extrusion is carried out from a die and the plies are directlyjoined before leaving the exit of the die. Preferably, the plies areextruded intubular form with the inner ply being polyethylene orpolypropylene (or other polymer having a relatively low adherencetosaran) and the outer ply being saran. In an alternative preferredprocedure, three tubular plies are formed with the intermediate plybeing saran and the inner and outer plies being the same or differentnon-saran thermoplastic polymers, e.g., both are polyethylene orpolypropylene (or one of the inner and outer plies is polyethylene andthe other polypropylene).

As an example of the non-saran thermoplastic polymer which can beemployed as an outer coat (and inner coat) in extruding the saran therecan be used: other solid olefins, e. g., polyethylene, polypropylene,polybutylene; other polymeric hydrocarbons, e.g., polystyrene; celluloseesters, e.g., cellulose acetate, cellulose propionate, cellulosetrityrate, cellulose nitrate; polyvinyl acetate; polymethacrylates,e.g., polymethyl methacrylates, polybutyl methacrylate; polyvinylalcohol; polyvinyl acetals, e.g., polyvinyl trityral; polyallyl alcohol;polyallyl acetate; polyesters, e.g., polyethylene terephthalate(Dacron); polyamides, e.g., nylon.

The term saran is used in its normal sense to include normallycrystalline polymers, both homopolymers and copolymers containingvinylidene chloride.

As copolymerizable materials there canbe used vinyl chloride,acrylonitrile, vinyl acetate, ethyl acrylate, methyl methacrylate.Terpolymers can also be employed, e.g., a terpolymer of vinylidenechloride, dimethyl maleate and vinyl chloride. In general, thevinylidene chloride is at least 50 percent of the material in thepolymer.

Different sarans vary in thermal stability, depending upon such factorsas the purity of the resin, the composition of the blend in which theyare used, and the vinylidene chloride content of the polymer. it will beobvious that variations in the stability of the saran polymer used will,to a considerable extent, control the nature of the non-saranthermoplastic polymers which can be utilized in the present invention.

In the illustrative examples a copolymer of about percent vinylidenechloride and 25 percent vinyl chloride was employed.

When the laminate tubular product is hot blown after leaving the die, itis not oriented substantially, although there is some bilateralstretching (alternatively, extrusion can be carried out without anystretching). The outer and/or inner layer of thermoplastic non-saranpolymer can be removed to produce a saran tube or film with improvedproperties. The thermoplastic polymer layer or layers serve to supportthe saran and permit the formation of very thin saran films. Inaddition, there is obtained a saran film having improved characteristicsas compared to film produced by conventional hot blown techniques. Thesaran film produced by the instant invention is free from blemishes dueto die scratches or mechanisms conventionally employed for handlingextruded saran film. In addition the saran film has greater elongation,better tear resistance, less tack, less shrink when heated and greaterclarity when compared with oriented saran made by conventional hot blowntechniques from the same blended polymer.

The outer thermoplastic plies can be stripped from the saran at anypoint after the saran layer is substantially crystalline followingextrusion. The stripped thermoplastic plies can be wound as film onrolls and used as such or can be reprocessed. When a two-ply tubularsystem is employed with a thermoplastic layer on the outside and with asaran layer inside, the outer layer may be slit and stripped from theinner tubular layer. In such a case, precautions must be taken toprevent the innermost saran faces from bonding one to another when thetubing is collapsed, since freshly extruded saran is generally verysticky. Dusting or coating the innermost surface with anti-blockingcompound is one accepted method of overcoming this problem.

The saran layer above can be employed as tubing or can be slitlongitudinally and employed as film. In the latter case the saran layercan be cut at the same time or later than the thermoplastic layer.Obviously, if the two-ply tubular system employs a saran layer outsidewith a thermoplastic layer inside the saran layer can be out prior tocutting the thermoplastic ply although normally this is not asconvenient.

The term stripping is intended to include any means employed forseparating the saran ply from the thermoplastic plies.

When a flattened laminated tubular product is produced, it is possibleto separate the plies by employing knives or cutting edges to cut all ofthe plies along the edges of the flattened multi-ply tubing, thenceseparating the plies and winding upon individual rolls. The flatthesaran center ply by passing the tube through hot.

water.

The unoriented saran film prepared according to the invention generallyhas a shrink of 1 percent to percent in the transverse direction and ashrink of 2 percent to percent in the longitudinal direction, is devoidof pinholes and die scratches, has a haze of not over 7 percent and atensile strength of 2500 pounds per square inch to 4500 pounds persquare inch and an elongation of 200 percent to 300 percent and a tearstrength of at least 50 grams per mil at a temperature of 23 C.

When colorant or other additives is added to the saran ply, the clarity,of course, will be affected, but the other properties are substantiallyunaffected.

The invention will be best understood in connection with the drawingswherein:

FIG. 1 is a sectional view of one form of die suitable for use in theinvention;

FIG. 2 is a sectional view of a tubular laminate product of the tapeproduced by the invention;

FIG. 3 is a schematic illustration of the invention;

FlG. 4 is a schematic illustration of the process for separating tubularlaminate into individual film plies;

FIG. 5 is a schematic illustration of an alternative form of theinvention (omitting the stripping step);

FIG. 6 is a schematic illustration of an alternative form of theinvention (omitting the stripping step); and

HO. 7 is a schematic illustration of an alternative subsequenttreatment.

It is important that all portions of the die through which the moltensaran travels be of streamlined con- I struction There should be nosharp corners or projecstreamlined or constructed of special material.Of

course, if desired, these portions of the die can be streamlined and allof the die may be made of nickel.

As is well known, the extrusion of saran poses problems due to thethermal instability of this class of materials. The rate ofdecomposition of saran is a function of both time and temperature; atincreasingly higher temperatures, the permissible time of exposurebecomes rapidly less. ln normal practice, extrusion temperatures for usewith the most stable blends of vinylidene chloride homopolymers and/orcopolymers are limited to a maximum of approximately 180 C.

In a relatively simple die of the essentially solid constructionsymbolized by FIG. 1, the maximum usable die temperature would belimited to 180 C. when saran was to be used in one of the plies. Thetemperature limitation dictates the types of thermoplastic ho- 4mopolymers and copolymers which could be utilized in this form of theinvention, such thermoplastic materials being limited to the class whichcan be extruded at die temperatures of 180 C. or lower. Typicalmaterials in this category include, but are not limited to, polyethyleneand polystyrene homopolymers and copolymers.

Shortening the time of exposure of saran to elevated temperatures makespossible the use of higher temperatures. This may be achieved by the useof suitable die configurations which will isolate the saran sections ofthe die from the non-saran sections up to the point where the multiplepolymer streams come together. The combined stream would be cooled asrapidly as possible after emerging from the die to prevent sarandecomposition.

An alternate method for combining saran with high melting resinsutilizes a die wherein the several parts of the die conveying thedifferent polymer streams are isolated one from another by theincorporation of hollow cavities, to be filled with circulating liquidsat the temperature required to protect the saran from overheating.Alternatively, the cavities can be connected to suitablecondensingmechanisms, and filled with liquids whose boiling points are low enoughto prevent saran decomposition. Excess heat applied to the outside ofthe die would create the desired temperatures adjacent to the cavitiesas the filling liquid boils. These would keep the isolated portions ofthe die below the temperatures at which the saran would decompose. Otherdevices for achieving the same purpose will readily occur to thoseskilled in the art.

With such precautions saran can be laminarly combined with materialswhich melt at temperatures as high as 200 C. or higher. High meltingmaterials suitable for such combining include, but are not limited to,polypropylene, polyacetals, polyesters, nylon.

While any conventional extrusion temperatures can be employed, e.g., C.to 160 C. for the saran and C. to 250 C. for the polyethylene, usuallythe temperatures of extrusion for the several plies will beapproximately the same.

ln the illustrative examples in connection with the drawings utilizingsaran and polyethylene, the extrusion temperature for all of the plieswas within 135 C. to C. The saran was compounded from 92 percent Saran925 (75 percent vinylidene chloride 25 percent vinyl chloride copolymeras manufactured by Dow Chemical Company, Midland, Mich), 7 percentdibutyl sebacate and 1 percent tetrasodium pyrophosphate, and thepolyethylene was Alathon l4 (molecular weight about 20,000 and density0.916, melt index 2 and manufactured by E. l. duPont de Nemours).

Other polyethylenes of high, medium or low density and prepared byeither high or low pressure processes can be employed. The polyethylenecan vary widely in molecular weights, e.g., from 7,000 to 35,000 orhigher.

I Referring more specifically to FIG. 1 of the drawings, there isprovided a die 2 having extruders (none shown) connected theretorespectively by adapters 4, 6, and 8. Molten polyethylene is transmittedfrom one extruder through adapter 4 to stream 10 and molten saran istransmitted from a second extruder through adapter 6 to stream 12.Molten polyethylene is transmitted from a third extruder through adapter8 to stream l4.'The adapters and the die sections are heatedsufficiently in order to maintain the polymers in a molten state byemploying conventional heating means, i.e., electric heaters, hot oil orsteam. Stream 12 joins stream 14 at juncture 16. Subsequently, streamit) joins the combined streams l2 and 14 at juncture 18. It will beobserved that the saran is sandwiched between the two plies ofpolyethylene. After all three plies have been united, they leave the dieat face 20. Air or gaseous medium is introduced through pipe 21 toinflate the multiwall tube as it leaves the die face 20.

Referring to FIG. 2, the product leaving the die as a continuous tube iscomposed of an outer polyethylene layer 24, a center saran layer 26, andan inner polyethylene layer 28. The outer layer can also be made ofpolypropylene (e.g., Hoechst polypropylene, density 0.90) or otherthermoplastic polymer or both the inner and outer layers can be made ofpolypropylene or other thermoplastic polymer by appropriate change ofmaterial fed to adapters 4 and 8.

While the multi-ply material need not be expanded as it comes from thedie, it is preferably expanded as shown in FlG. 3. Generally, it isexpanded 2 to 2.5 times as it leaves the die. Thus, very thin saranfilm, e.g., 0.1 to 0.5 mil, having a coating of 0.1 to 2.0 milpolyethylene or other thermoplastic polymer on each side can be readilyprepared.

Referring to FlG. 3, there is provided a die 30. Saran is supplied tothe die from extruder 32 and polyethylene is supplied to the die fromextruder 34 and 35 in order to make a three-ply(polyethylene-saranpolyethylene) laminate. Extruder 34 and 35 may bereplaced by a single extruder feeding two adapters in order to supplypolyethylene for both the innermost and outermost plies.

The tubular saran ply and the tubular polyethylene plies are joinedwithin the die in the manner shown in FIG. 1 with a polyethylene plybeing on the outside, the saran ply being in the middle and the otherpolyethylene ply being the inner layer. As is conventional in thepolyethylene extrusion art, a cooling ring 36 with air circulatngtherefrom is provided near the exit of the die with air provided byblower 37. Tube 38 having an outer ply of polyethylene and a middle plyof saran and an inner ply of polyethylene as it leaves the die face inan upward direction is formed into a bubble with the aid of air or otherentrapped gas maintained between the die face and deflate rolls 44. Theposition of the bubble is regulated by guiding devices 42. The blowntubing generally has a shrink of l to percent in a transverse directionand 1 percent to percent in a longitudinal direction at 85 C. (This istrue for both twoand three-ply tubular products.) In a specific examplewith the three-ply polyethylene-saranpolyethylene, the shrink was 2percent transversely and 12 percent longitudinally. The laminated bubble38 is flattened at the upper end with the aid of flattened plates 46.The flattened three-ply tubing is wound on a windup roll 49.

After storing the supply rolls for a sufficient time to allow forcrystallization of the saran, the individual plies may be separated andwound on individual supply rolls as film. If the individual saran ply iswound on a roll before crystallization, the adjacent plies will adhereto each other and destroy the film upon attempted subsequent separationfor use.

In FIG. 4 is shown a schematic representation of a method for separatingthe individual plies of a multi-ply tubular product which is wound on asupply roll such as 49 in FIG. 3.

In FIG. 4 the flattened three-ply tubing in the form of a tape 50 fromsupply roll 51 passes under circular knives 52 which work in conjunctionwith press roll 53 and positioned near the edges of the flattenedmulti-ply tube so that each of the folded edges ofthe flattenedthree-ply tube 50 are cut. The outer polyethylene plies 54, 56 and theinner polyethylene plies 58, 60 of the tape are continuously strippedfrom the middle saran plies 62 and 64. The polyethylene plies 54, 56,58, 60 pass to wind-up rolls 66, 68, 70, 72, respectively, and the saranplies 62 and 64 pass to windup rolls 74 and 76. The trimmed off portion78 is removed as scrap in any conventional manner, i.e., air suctionduct.

If sufficient time has not elapsed for crystallization of the saran ply,slip sheets of nonadhering material, i.e., paper, must be used in orderfor the saran plies not to adhere to the adjacent surfaces on the winduprolls 74 and 76. Obviously, if the process of FIG. 3 and F IG. 4 are tobe performed concurrently, a system of slip sheeting the saran supplyrolls 74 and 76 must be used. An alternate method which may be employedis an inventory system between deflate rolls 44 and the windup rolls 74and 76 in order to allow the saran film time for crystallization, whichtime was approximately thirty minutes at room temperature.

In a specific example utilizing the process shown in F IG. 3, thecircular die orifice had an outside diameter of 25.4 centimeters, aninside diameter of 25.2 centimeters. Extruder 35 was eliminated andextruder 34 supplied the polyethylene for both of the outer plies of thelaminate. Saran, compounded as indicated above, was extruded at a rateof 40 pounds per hour in extruder 32 and polyethylene (Alathon 14 fromE. l. du- Pont de Nemours) was extruded at pounds per hour in extruder34. The maximum diameter of the bubble was 63 centimeters. The distancefrom the die orifice to the deflate rolls was 213 centimeters and thedeflate rolls rotated at a surface speed of 12.2 meters per minute. Thewindup roll 49 rotated at the same surface speed as the deflate rolls.After crystallization of the saran, the individual film plies wereseparated and the finished single layer saran film had a thickness of0.2 mils, and the polyethylene film layer had a thickness of 0.2 milsand 0.2 mils, respectively.

The saran layer of the film laminate thus formed had a transverse shrinkof 2 percent and longitudinal shrink of 7 percent. To those familiarwith the art, this film is substantially unoriented and representsnormal shrinkage for hot blown film. The subject invention thusrepresents a novel method of producing a very thin, unoriented, saranfilm. This is made possible by having the saran between two layers ofhot thermoplastic so it does not cool rapidly and become oriented. Whenhot blowing plain saran by other known methods, the rapid cooling andnature of the material results in an appreciable amount of orientationand therefore subsequent ability to shrink.

Physical properties of the saran film produced by the example above andthe laminate containing the saran film ply produced by the example abovewere as follows:

L Longitudinal FIG. illustrates an alternative stretching procedureemploying a two-ply polyethylene-saran tube, with the saran being theinner ply. Polyethylene and saran are fed into die 80 and the twostreams are joined within the die in a manner similar to that shown inFIG. 1, with the saran being on the inside. Instead of being expandedinto a bubble, the two-ply tubing emerges from the die as an unexpandedtube 82. The tube passes through cooling bath 84, e.g., water maintainedat room temperature.

As the tube passes through the cooling bath, a liquid 86 inert to saran,e.g., mineral oil, is recirculated through ducts 88 and 90 in the diehead into the newly formed tube to prevent the walls of the tube fromsticking together when the tube is pressed flat. The extruded tub had awall thickness of 0.25 millimeters and a diameter of 19.0 centimeters.The extruded tube was pressed flat to form a tape 94 by passing througha pair of driven rolls 92 rotating at a surface speed of 3.35 meters perminute. The tape was fed over idle roll 96 into hot oven 98 maintainedat 100 C. and fed through a pair of pinch rolls 100 at outlet end ofoven 98, rotating at a surface speed of 3.38 meters per minute. Air orother gas is introduced into the heated tape to form a gas bubble 102between the pinch rolls 100 and a pair of upper deflate rolls 104 in theair and rotating at a surface speed of meters per minute. The bubble isgradually flattened with the aid of converging rollers 106. Followingthe collapse of the bubble by deflate rolls 104, the flattened tubing ortape 108 is fed to the roll 110 on which it is wound.

The bilaterally oriented product had a thickness of 0.2 mils in thepolyethylene ply and 0.5 mils in the saran ply.

When-it is desired to form film from wound flattened tubular tape suchas that wound on roll 110 in FIG. 5, this can be done by simultaneous orprogressive cutting. The wound-up supply roll of multi-ply material maybe placed upon an apparatus similar to FIG. 4 and the multi-ply layersseparated and wound upon individual supply rolls.

Another illustrative example of the instant invention is shown in FIG.6. Saran is supplied to the die from extruder 132 and polyethylene issupplied to said die from extruder 134 through a two-stream adapter. Thesaran ply and the two polyethylene plies are joined within the die asshown in FIG. 1 with one polyethylene ply being on the outside, thesaran ply being in the center, and the other polyethylene ply on theinside. The die is heated in conventional fashion by means not shown.Tube 138, having an outer ply of polyethylene, an intermediate ply ofsaran and an inner ply of polyethylene as it leaves the die face in adownward direction is drawn over a cylindrical cooling and formingmandrel 140. A water-cooling ring 142 with water circulating therefromis provided opposite to the shoe and around it, and water impinges onthe exterior surface of the tube 138 and cascades downward into tank146. Overflow 147 maintains the level of the water in tank 146. The tube132, having an outer ply of polyethylene, a middle ply of saran and aninner ply of polyethylene, is drawn down by the drive rolls 144.

In a specific example, the circular die orifice had an outside diameterof 25.4 centimeters, and a inside diameter of 25.2 centimeters.

Polyethylene was extruded at a rate of pounds per hour from extruder134, while saran was extruded at.40 pounds per hour from extruder 132.

A tube was extruded downward over a sizing mandrel through pinch rolls144 rotating at a surface speed of 3.05 meters per minute. The diameterof the cooling mandrel was 19 centimeters, and the length was 10.1centimeters, and the upper end of said mandrel was located 15.2centimeters from the die face. Cooling water was supplied to the coolingmandrel with an inlet temperature of 10 C. and outlet temperature ofabout 12 C.

The substantially unoriented three-ply tape 148 emerging from the pinchrolls 144 had an overall thickness of 10 mils and was fed via idler roll150 to hot oven 158 with ambient temperature of C. The tape was fed froma pair of pinch rolls 162 rotated at a surface speed of 3.1 meters perminute and located at the outlet to the oven, to a pair of deflate rolls164 in the air, and rotated at a surface speed of l 1 meters per minute.Air was introduced into the tape to form a three-ply gas bubble 166between the pinch rolls of oven and the upper deflate rolls 164. Thefilm was cooled by the external air. The bubble was gradually flattenedwith the aid of converging rolls 168. The maximum diameter of the bubblewas 68.5 centimeters The transverse stretch was 5 to l and thelongitudinal stretch was 3 to 1. The finished tubing had a total wallthickness of about 0.7 mil. The thickness of the individual portions ofthe finished tubing were:

Outer polyethylene 0.40 mil Saran 0.20 mil Inner polyethylene 0.l6 milThree-Ply Laminate (polyethylenesaranpolyethylene) Tensile Strength T7,600 (lbs per sq in) L 6,300 Shrink at 96C. T 6] L 54 It has been foundthat by combining the plies, e.g., polyethylene-saran-polyethylene,before extrusion from the die, there is obtained a better bond betweenthe several layers than would be obtained by a laminate made fromself-supporting film layers combined after forming each layer. This isimportant in subsequent processing prior to stripping, e.g., in theblowing or biaxial orientation step. The bond between the plies in thehot blown bubble makes it possible to produce very 2 thin saran plieswith uniform gauge and uniform characteristics.

Tests were made upon the finished laminate produced by the instantinvention to measure the degree of adhesion or'cling shear strengthbetween the saran ply and the polyethylene ply as compared to theadhesion between a saran ply and a polyethylene ply placed in intimatecontact by using pressure rolls, but no adhesive. The specimens wereprepared by starting the separation of the plies and measuring theamount of pull necessary to separate in-shear a unit cross-section ofthe specimen laminate. The individual ply of the specimen properlyprepared was placed in the jaws of an Instron Tensile Tester with thejaws having an initial separation of 5.08 centimeters and the laminatebetween the jaws. The load was observed at the point of shear separatingthe plies. On test'samples of a saran and polyethylene laminate producedaccording to the illustrative example shown in FIG. 2, an average valueof 390 grams per square centimeter was obtained. Similar tests upon alaminate produced by placing a saran ply of identical gauge andidentical polymer composition in contact with a ply of polyethylene ofidentical gauge and polymer composition with 500 pounds per square inchpressure at 22 C. for 5 minutes produced an average value of 90 gramsper square centimeter. When this latter test was repeated using the samepressure but a temperature of 65 C. and times up to 1 minute, theaverage value of 170 grams per square centimeter was obtained.

Irradiation may be used to advantage in the instant invention to make itpossible to use a minimum thickness of polyolefin material in themulti-ply tube and obtain a laminate and/or a saran ply with greaterclarity and surface gloss than heretofore obtainable by known processes.

The substantially unoriented three-ply tubular tape such as 148 emergingfrom deflate rolls 144 of FIG. 6 can then be irradiated and bi-axiallyoriented as shown in FIG. 7, For simplicity in FIG. 7, roll 200represents a supply of substantially unoriented three-ply tubular tape.The tape being fed from the supply roll 200 could be replaced by tubulartape 148 of FIG. 6 and a continuous process employed. Due tocrystallization time of the saran layer as mentioned above, theirradiation must take place within about minutes after extrusion. In aspecific example employing the method shown in FIG. 7, the tape from thesupply roll 200 was of three tubular plies and was fed through feedrolls 202 into a vault 2 which houses and encloses an electron beamgenerator 206 (e.g., a 2 million volt General Electric resonanttransformer). With the aid of feed rolls 208, the tape wascaused topassthrough the electron beam of the generator. The total irradiation dosagecan be varied and was 12 megarad in the specific example. Followingirradiation, the tape was fed by feed rolls 210 rotated at a surfacespeed of 3.35 meters per minute to an oven 212 at 200 C. The tape wasfed from a pair of pinch rolls 2M rotated at a surface speed of 3.39meters per minute at the outlet of the oven 212, to a pair of deflaterolls 216 in the air and rotated at a surface speed of 10.1 meters perminute. Air or other gas is introduced into the heated tape to form athreeply gas bubble 218 between the pinch rolls 2M and the upper deflaterolls 216. The bubble is cooled by the outside air and was graduallyflattened with the aid of converging rolls 220. The transverse stretchwas 4 to l O and the longitudinal stretch was 3 to l. The finishedtubing had a wall thickness of about 0.018 millimeters. Following ,thecollapse of the bubble by deflate rolls 216, the flattened tubing 222was fed to roll 224 on which it is wound.

The physical properties of the irradiated oriented saran film ply aboveand the three-ply laminate made in the above examples were as follows:

Saran Film Ply Three-Ply Laminate (Polyethylene 0.4 Gauge 0.3 (Saran 0.3(mils) (Polyethylene 0.3 Modulus at 22C. 23,900 22,300 (lbs per sq in)Shrink at 96C. T 45 T 54 L 42 L 46 Haze 1.] 7.3 Reflectance 0.8 l .3

-type electron accelerator, e.g., one operated at 2,000,000 volts with apower output of 500 watts. Alternatively, there can be employed othersources of high energy electrons, such as the General Electric 2,000,000volt resonant transformer or the corresponding 1,000,000 volt, 4kilowatt, resonant transformer. The voltage can be 10,000 or 2,000,000or 3,000,000 or 6,000,000 volts or higher. The irradiation is usuallycarried out between 1 megarad and megarad, with a preferred range of 8megarad to 20 megarad. Irradiation can be carried out conveniently atroom temperature, although higher and lower temperatures, e.g., 0 C. to60 C. can be employed.

The biaxially unoriented multi-ply tubing formed (either irradiated orunirradiated) can undergo a transversestretch of percent to 900 percent,preferably 300 percent to 500 percent, and a longitudinal stretch of 100percent to 700 percent, preferably 300 percent to 500 percent. It isextremely difficult to continuously biaxially orient unirradiatedpolyethylene by such a bubble stretching technique since the bubblenormally breaks in a short period of time. However, by employing atwo-ply polyethylene-saran tube or a three-plypolyethylene-saran-polyethylene tube, it is possible to extend theperiod of continuous stretching considerably.

Some of the laminate products produced as an intermediate step in thepreferred process have improved characteristics which have beenheretofore unknown, particularly those laminates made up of polyolefinand saran. Polyolefin films have been widely used in packagingapplications. However, the lack of vapor barrier characteristics hasprevented the application of these films to packages where low oxygenand moisture vapor transmission are required or desired, as in thepackaging of foods. Unoriented polyethylene-saran,polyethylene-saran-polyethylene, polypropylene-saran, orpolypropylene-saran-polypropylene laminates as produced by the processdescribed in conjunction with FIG. 2 were particularly interesting.Economically, this product is of great importance because of therelatively thin laminates which it is possible to obtain. In addition,the degree of intimate contact between the plies obtainable by theextrusion and combining of the molten plies within the die results in afilm laminate which can be used for many packaging applications withoutfurther treatment. It is well-known that such laminates of polyethyleneand saran heretofore made by combining self-supporting sheets of each ofthese materials or coating self-supporting polyethylene film with acoating of saran from solution has required modification of thepolyethylene surface to effect surface adhesion of the plies. In thelaminated product by the instant invention, the adherence of the pliesissufficient to maintain them in intimate contact during use. However,once the edges of the self-supporting individual plies are separated,they may be stripped from the adjacent plies of the laminate withoutdifficulty.

Similarly, the biaxially oriented laminated product as produced by theprocess described in connection with FIGS. 4, 5, and 6 has unusualproperties which will make them useful for packaging applications.

It is also possible to have more than three plies, e.g., there can beformed a five-ply polyethylene-saranpolypropylene-saran-polyethylenetubing.

While preferably the plies are formed as tubing, it is possible to formthe multi-ply product directly as sheeting by employing a slit die. Insuch case the saran ply can be stripped from the other ply or plies bycutting or any of the other methods proposed above.

The polyethylene or other thermoplastic polymer, particularly in thethree-ply construction, prevents the saran from sticking to itself whenwound into a roll prior to stripping. The need for inventory equipmentto allow for time of crystallization to render the saran non-tacky isthus eliminated.

As previously mentioned, very thin films can be formed. Thus, athree-ply polyethylene-saranpolyethylene having a total thickness of 30mils (l mils'per layer) can be hot blown as it comes out of the die toan overall thickness of 1.5 mil (0.5 mil per layer) or less. The severalplies need not be of the same thickness. The saran ply can be eithergreater or smaller in thickness than the polyethylene or polypropyleneply or plies. For examples, the saran ply can be 10 percent to percentof the thickness of the thermoplastic polymer ply in a two-ply product.

It is possible to incorporate dyes and pigments into one or more of thelayers to obtain novel color effects. Thus, a dye, e.g., ED. plus C Red'32, could be incorporated in the center saran layer while omitting itfrom the external olefin polymer layers. This technique can be used tospecial advantage to lock in a pigment or dye which would otherwisebleed.

The products of the present invention can be used as conventionalpouches, boil-in-bag pouches (particularly if irradiated), turkey bags,shrinkable pouches (particularly if the multi-ply product is racked),grease resistant pouches, rust and mold inhibiting films, pouches andbags, red meat protective film, pouches and bags, moisture controlfilms, vacuum forming raw material, window films, improved weatheringfilms, improved abuse resistant films at a wide range of temperatures,drum and other container liners, bread wraps, wrapping for cheese(particularly a sandwich of polyethylene-saran-polyethylene to give lowpermeability), containers which are resistant to gas and liquidtransmission for medicine, pharmaceuticals, cosmetics, perfumes and thelike, pipe line wrapping, floor tiles, bottle cap liners, e.g., crowncap liners.

The term film as used herein is generic to both tubing and sheet stockunless a contrary meaning is clearly indicated.

We claim:

1. A substantially unoriented crystalline film made from a thermoplasticcopolymer of vinylidene chloride and at least one copolymerizablemonomer wherein the vinylidene chloride is at least 50 percent of thematerial in the copolymer, said film having a shrinkability at 96C of 1to 5 percent in the transversedirection and 2 to 10 percent in thelongitudinal direction, a haze of not over 7 percent, and an elongationof at least 100 percent in both the transverse and longitudinaldirections, said film having been made by coextruding said copolymer asa melt between outer plies of thermoplastic polymers through a die so asto produce a copolymer film between the outer plies which issubstantially devoid of pinholes and scratches and has low oxygenpermeability and thereafter separating said outer plies from saidcopolymer film.

2. The film of claim 1 wherein said film has been irradiated with highenergy electrons to a dosage of l megarad to 75 megarads.

3. A biaxially oriented crystalline film made of a thermoplasticcopolymer of vinylidene chloride and at least one copolymerizablemonomer, wherein the vinylidene chloride is at least 50 percent of thematerial in the so polymer, said film having an average thickness ofless than 0.3 mil and having a shrinkability at 96C of 100 to 500percent in the transverse direction and 100 to 700 percent in thelongitudinal direction, said film having been made by coextruding saidcopolymer as a melt between outer plies of thermoplastic polymer meltsthrough a die, cooling and stretching to orient so as to produce acopolymer film between the order plies which is substantially devoid ofpinholes and scratches and has low oxygen permeability and thereafterseparating said outer plies from said copolymer film.

4. The film of claim 3 wherein said film has been irradiated with highenergy electrons to a dosage of 1 megarad to 75 megarads after coolingbut before stretchmg.

5. The film of claim 3 wherein said film has a haze of less than 2percent and an average shrink of more than 30 percent in both thetransverse and longitudinal directions.

2. The film of claim 1 wherein said film has been irradiated with highenergy electrons to a dosage of 1 megarad to 75 megarads.
 3. A biaxiallyoriented crystalline film made of a thermoplastic copolymer ofvinylidene chloride and at least one copolymerizable monomer, whereinthe vinylidene chloride is at least 50 percent of the material in thecopolymer, said film having an average thickness of less than 0.3 miland having a shrinkability at 96*C of 100 to 500 percent in thetransverse direction and 100 to 700 percent in the longitudinaldirection, said film having been made by coextruding said copolymer as amelt between outer plies of thermoplastic polymer melts through a die,cooling and stretching to orient so as to produce a copolymer filmbetween the order plies which is substantially devoid of pinholes andscratches and has low oxygen permeability and thereafter separating saidouter plies from said copolymer film.
 4. The film of claim 3 whereinsaid film has been irradiated with high energy electrons to a dosage of1 megarad to 75 megarads after cooling but before stretching.
 5. Thefilm of claim 3 wherein said film has a haze of less than 2 percent andan average shrink of more than 30 percent in both the transverse andlongitudinal directions.